Preservation of vegetable cellulosic material



Patented Dec. 4, 1934 r,

PRESERVATION OF VEGETABLE CELLU- LOSIC MATERIAL Carl H. Siever, Oak Park, Ill.

No Drawing. Application October 6, 1930, Serial No. 486,717

1 Claim.

My invention relates to the preservation of vegetable cellulosic material, particularly the preservation of wood when used in the form of railroad crossties, telephone poles, structural timber, and the like.

The treatment of wood to preserve the same is directed in general to two main ends, namely the protection of the wood from biological organisms such as fungi, and the mechanical protection of the wood, as for example, by waterproofing. In certain respects most treatments have both ends in view, and this is particularly true of the present most widely used method which consists in the impregnation of the wood with creosote. Where woods are treated with fungicides alone, the toxic substance which acts as a fungicide is generally dissolved in water. Even though heat and pressure are employed,

forcing the impregnating substance into the fibers or cells of the wood, impregnation seldom reaches more than a quarter to a half an inch in depth. This is the maximum penetration obtained, evenwith temperatures as high as 200 degrees F and'a pressure as high as 200 pounds per square inch, for periods of time varying from 3 to 6 hours. Accordingly, it may be said that the penetration of one-half an inch is about the maximum that can'be expected, because if higher temperatures are employed there is a tendency to decompose the wood, and if pressures in excess of 200 pounds are used, the walls of the wood fiber will tend to collapse. I

' Theprincipal object of my present invention is the treatment of vegetable cellulosic substances by an improved process. 1

Another object is to secure a deeper penetration of treating substances into the wood.

solvents in the treatment of wood in order toob- Another object is greatly to improve the life of wooden article's. Other objects and features of the invention will be apparent from a consideration of the following detailed description.

In general, my invention consists in the use of relatively low surface tension volatile organic materials used, they can be of a type to impart water-proofing properties to the wood, or to convey toxic substances alone to the wood, or they may be combinations of these two. As to the water-proofing substances, these may be petroleum oils, various grades of distillate, creosote, or the like, Examples of toxic compounds capable of being dissolved in the alcohol or other solvent are mercuric chloride, zinc chloride, and many other similar compounds, large numbers of which are known to those skilled in the art. I have found that the water-proofing substances and toxic materials may be used together with any selected solvent, such as acetone, and the acetone will aid in causing a deep penetration of both the toxic material and the water-proofing material. I have discovered that these volatile organic liquids having low surface tension characteristics, and particularly liquids which are readily miscible with water, possess relatively high penetrating power of wood and other vegetable fibrous materials. I have observed that the rate of penetration into dry wood, paper and the like, by a volatile organic liquid which is readily miscible with water, is roughly inversely proportional to the surface tension of that particular liquid for a given temperature and pressure. For example, I have found that both methyl alcohol and ethyl alcohol which have surface tensions of approximately 22 dynes per centimeter at 20 degrees centigrade and at atmospheric pressure will penetrate dry wood or paper about three times more rapidly than will water with a surface tension of 72% dynes per centimeter at 20 degrees centigrade and at atmospheric pressure. Acetone, with a surface tension of 23.7 dynes per centimeter at 20 degrees centigrade, will likewise penetrate dry wood or paper approximately three times more readily than will water under the same conditions of temperature and pressure.

In the course of numerous experiments, I have found that solutions of certain toxic substances dissolved in one or more of these volatile organic liquids or solvents can be made to penetrate wood and the like much more readily than aqueous solutions can be made to penetrate the same vegetable fibrous materials under the same conditions of temperature and pressure, and that the organic solvent, by virtue of its easily volatile nature, can be readily and commercially recovmuch greater concentrations of these toxic materials can be introduced into wood than is possible in the case of the corresponding aqueous solutions regardless of howigreat may be the temperature, pressure or duration of the treatment.

On a commercial scale, the usual apparatus and general inethods of application for the pressure treatingfand preserving of wood are applicable to my process; the only additional equipment which is essential is an eflicient condenser attached to the pressure tank for the recovery of the volatile organic solvent afterthe wood has been impregnated. I prefer to use a readily volatile organic liquid, such as methyl alcohol, ethyl alcohol, acetone, etc., rather than a higher boiling material for the reason that I may conveniently and economically recover this more volatile solvent by simple distillation at relatively low temperatures and subsequent condensation of the vapors from the impregnated wood or other fibrous material while the latter remains in the impregnating pressure tanks. The critical temperature and the critical pressure of any volatile solvent which I may use, such as methyl alcohol, ethyl alcohol, or acetone, are sufficiently high that these materials will remain in liquid state under the temperatures and pressures commonly employed in the usual wood-preserving pressure treatments.

The following examples will serve to illustrate my process.

Example I I may dissolve, say one percent by weight of mercuric chloride in acetone and impregnate wood with this solution under conditions of, say a temperature of 200 degrees Fahrenheit, a pressure of 200 pounds per square inch and for a period of three hours, using the usual pressure treating tanks commonly employed for this purpose, but fitted with a valve leading to any suitable condenser for condensing and recovering the acetone. After the wood has received the desired penetration by the preservative solution, I may open the valve leading to the condenser and allow the acetone to distil into the condenser, and from the condenser the acetone may be passed in liquefied state to any suitable receiving tank where it may be treated with a further quantity of mercuric chloride and used again in subsequent woodpreserving treatments. While acetone has a boiling point of only 56 degrees centigrade at ordinary atmospheric pressure, it will remain in liquid state at 100 degrees centigrade (212 degrees Fahrenheit) under pressures as low as 55 pounds per square inch (3.67 atmospheres).

Example II I may dissolve five percent by weight of zinc chloride in methyl or ethyl alcohol and impregnate Wood with this solution according to the process as outlined in Example I.

Example III I have found that by mixing coal tar creosote with a volatile organic solvent which is readily miscible with water, considerably better woodpenetrations can be obtained under given conditions of time, temperature, pressure and concentration with such mixtures than can be obtained with coal tar creosote alone which is practically immiscible with water. I have found that if methyl or ethyl alcohol or acetone is added to coal tar creosote, the mixture will dissolve an appreciable quantity of water, the amount of dissolved Water increasing with each increase in temperature of solution as well as with each increase in alcohol or acetone content. Thus a mixture of equal parts by weight of acetone and creosote will dissolve about five percent of water at 160 degrees Fahrenheit, the amount of water dissolved increasing with temperature and acetone content. This water-dissolving property of acetone-creosote mixtures is important in connection with the penetration of wood since it facilitates ready wetting of the wood fibers and hence increases penetration by the wood-preserving solution. I have also found that the toxic properties of mixtures such as acetone-creosote solutions can be greatly increased over those of coal tar creosote alone by dissolving certain toxic substances in a given mixture which substances are readily soluble in the mixture, but which are ordinarily insoluble or practically insoluble in the undiluted creosote.

To illustrate my process, I may add a predetermined quantity of mercuric chloride, say one percent by weight, to a mixture consisting of equal parts by weight of acetone and coal tar creosote.

I may impregnate wood with this solution undera valve leading to any suitable condenser forcondensing and recovering the acetone. After the wood has received the desired penetration by the: preservative solution, I may open the valve'lead ing to the condenser and allow the acetone to dis till into the condenser, and from the condenser I may transfer the acetone in liquid state to any suitable receiving tank where it may be treatedwith further quantities of creosote and mercuric chloride and used again in subsequent wood-pre-' serving treatments.

As compared with water, the relatively low latent heats of vaporization, the low specific heats,"

the low densities and the comparatively low boil- .ing points of these solvents make the vaporlzation and recovery of these materials very quick and economical when costs are computed on a gallon basis.

little or no appreciable loss other than the small amount oi. vapors remaining in the pressure tanks when the treated wood is removed therefrom. The recovered solvent may be used over and over Practically a complete recovery of the solvent should be readily accomplished with.

again in subsequent wood-preserving treatments. I do not wish to confine my process to the use of the above mentioned volatile organic liquids, but may employ any other organic liquid or combination of liquids which will serve my purpose as set forth in this specification. I may also employ any other toxic substance or substances which may be applicable to my process of preserving wood or any other vegetable fibrous ma-- terlal. Neither do I confine my invention to the use of the standard equipment now in use by the wood-preserving industry, but may use any suitable equipment which may be developed or which is already in use providing, of course, that suchequipment is adaptable and suitable to my process. When the invention is practiced according to.

the third example given above, and in which toxic compounds are added to the mixture of creosote and solvent, 2. final wood product is produced in which very deep penetration of the wood fibers by the creosote takes place, and in which the creosote is admixed with finely divided i toxic material, and as is readily understood by those skilled in the art, such toxic material may be of a type not normally soluble in the creosote, but which might be soluble in the solvent used with the creosote. I have found that I obtain a much better product and one which is considerably more resistant to the propagation of fungi than any which I have been able to develop or produce by any other simple impregnating process. As to the properties of creosote when used alone with the, solvent, it is well known that creosote not only has water-proofing value, but also contains toxic materials, making it in many respects, a fungicide. This is particularly true with certain types of creosote.

I have described my invention in considerable 

